1. Field of the Invention
The present invention relates to polypropylene resin compositions and to their injection foamed articles. Particularly, it relates to polypropylene resin compositions such that they exhibit good moldability and they can afford injection foamed articles having good appearance when they are used for the production of injection foamed articles, and to their injection foamed articles.
2. Description of the Related Art
Polypropylene resin has conventionally been used as material for foaming because of their light weight and superior heat insulation property.
For example, JP 07-138323 A discloses a propylene-based polymer for foaming, especially for extrusion foaming, from which foamed articles having good surface appearance and good heat insulation property can be obtained with good moldability, the polymer comprising a propylene-based polymer having an intrinsic viscosity of from 0.5 to 1.9 dl/g and a ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), Mw/Mn, of 6 or more and a propylene-based polymer having an intrinsic viscosity of from 4.5 to 9.0 dl/g.
JP 10-330560 A discloses a resin composition for foaming, the composition being prepared by blending a foaming agent to a crystalline polyolefin resin composition prepared by melt-kneading a propylene-α-olefin copolymer, polyethylene, elastomer and a crosslinking agent.
JP 2002-173564 A discloses a modified polypropylene resin composition having an improved melt characteristics obtained by blending a radical generator to a polypropylene resin composition composed of a high molecular weight polyethylene (co)polymer having an intrinsic viscosity of from 25 to 60 dl/g and a polypropylene (co)polymer having an intrinsic viscosity of from 4 to 12 dl/g and melt-kneading them. A foamed article obtained from this resin composition is also disclosed.
In use in injection foam molding of the polypropylene resin compositions disclosed in the publications cited above, further improvement in moldability of the polypropylene resin compositions and in appearance of resulting injection foamed articles has been demanded.
Under such circumstances, the present invention is intended to provide polypropylene resin compositions such that they exhibit good moldability and they can afford injection foamed articles having appearance when they are used for the production of injection foamed articles and also provide their injection foamed articles.